Keep in mind folks that it's not like there's aliens swarming throughout Providence right now. It's more of an easter egg than anything, a bit of non-'canon' fun like the crappy meal and all that. I for one and going to pretend that witches from now on are simply humans infected with an alien virus that lets them do force **** or something.
In all seriousness, even if one were to treat it as canon, I personally don't mind a mixing of genres that much so it's whatever to me. A little science fiction here, a little fantasy here, all good in the hood, it just depends on how good the story, or in this case, the atmosphere, is crafted.